The Microcellular Structure of Injection Molded Thick-Walled Parts as Observed by In-Line Monitoring

Abstract

The aim of the study was to detect the influence of nitrogen pressure on the rheological properties and structure of PA66 GF30 thick-walled parts, produced by means of microcellular injection molding (MIM), using the MuCell® technology. The process was monitored in-line with pressure and temperature sensors assembled in the original injection mold. The measured data was subsequently used to evaluate rheological properties inside an 8.4 mm depth mold cavity. The analysis of the microcellular structure was related to the monitored in-line pressure and temperature changes during the injection process cycle. A four-times reduction of the maximum filling pressure in the mold cavity for MIM was found. At the same time, the holding pressure was taken over by expanding cells. The gradient effect of the cells distribution and the fiber arrangement in the flow direction were observed. A slight influence of nitrogen pressure on the cells size was found. Cells with a diameter lower than 20 µm dominate in the analyzed cases. An effect of reduction of the average cells size in the function of distance to the gate was observed. The creation of structure gradient and changes of cells dimensions were evaluated by SEM images and confirmed with the micro CT analysis.

High-Performance of a Thick-Walled Polyamide Composite Produced by Microcellular Injection Molding

“…The influence of the moldings wall thickness on mechanical properties, like tensile and bending strength, Young’s modulus, impact resistance, and hardness of PA66 GF30 porous composites have been investigated and analyzed. These studies are a continuation of a previously published paper [ 20 , 22 ] on PA66 GF30 thick-walled elements obtained by MuCell ® technology. Foamed moldings with no defects were obtained without applying the holding phase.…”

“…The observed effect was caused by large cell dimensions (0.067 to 0.098 mm size), which dominated the core and transition zone of foamed parts. An original injection mold and measurement method were applied in the study of the MuCell ® technology processability [ 21 , 22 ]. Pressure and temperature sensors were used to online measurement apparent viscosity, shear stress, and a shear rate of melt directly in the injection mold cavity.…”

“…Therefore, it is justified to research in the field of the production of lightweight thick-walled elements from polymeric materials reinforced with short fiber. In the 2020 published paper, extensive results related to the production of thick-walled elements (6 mm and 8.4 mm) with the use of the MuCell ® technology were presented [ 22 ]. Obtained PA66 GF30 foamed parts characterized the advantageous cellular structure.…”

“…Foamed moldings with no defects were obtained without applying the holding phase. The results of the structural studies obtained in an earlier publication have been extended to explain the behavior of thick-walled, porous PA66 GF30 moldings due to the effects of static and dynamic external loads [ 22 ].…”

The Feasibility of an Internal Gas-Assisted Heating Method for Improving the Melt Filling Ability of Polyamide 6 Thermoplastic Composites in a Thin Wall Injection Molding Process

“…In injection molding, the selection of an appropriate cavity surface temperature is a key point in plastic processing, especially with thin products or molding processes with low viscosity materials, such as composites [1][2][3]. With a hot mold surface, the part quality will be improved, although the cycle time will be longer.…”